THE REACTIVATION MECHANISM OF ANCIENT OCEAN LANDSLIDES DURING HYDRATE PRODUCTION: A PRELIMINARY STUDY

Ancient landslides are widely developed in hydrate-rich areas in the northern continental slope of the South China Sea. Imprudent hydrate production may result in the reactivation of the ancient submarine landslides. In order to explore the mechanism of the ancient landslide reactivation induced by hydrate production, we analyzed the slope stability and instability modes of two typical ancient landslides: the underburden-type and the associated-type. The analysis accounted for the changes of the transient pore pressure and the soil shear strength during hydrate production within the limit equilibrium analysis framework. The results suggest that hydrate dissociation results in the reduction of the cementing strength and meanwhile, the released gas may be trapped below the ancient landslide body with low permeability, giving rise to a laterally extending high-pressure zone. The potential slip surface of the underburden-type reservoir goes through the ancient slip surface, showing a slide pattern. In the early stage of production, the slope stability decreases due to the pore pressure build-up. Then, during the middle and late stages of production, the slope stability recovers because of the secondary hydrate formation. The production would not trigger the ancient reactivation with the calculation configuration in this study. The slope stability of the associated-type reservoir is affected by both the soil strength reduction and the pore pressure build-up. Hydrate production from an associated-type reservoir may trigger the reactivation of the ancient landslide, showing a slump pattern.